ROR1 is a receptor for Wnt5a, which can induce non-canonical Wnt-signaling, activate Rho GTPases, and enhance leukemia-cell migration, proliferation, and survival. High-level expression of ROR1 can accelerate development and progression of leukemia in transgenic mouse models and associates with more aggressive disease and shorter survival of patients (pts) with CLL. CLL cells also express other developmentally-restricted Wnt5a-receptors, namely ROR2 and RYK, which can contribute to non-canonical Wnt-signaling in CLL. We hypothesize that elucidation of the structure-function-relationships involved in signaling by ROR1, ROR2, and RYK will define clinically relevant biomarkers for non-canonical Wnt-signaling and identify novel targets for therapy. Moreover, inhibition of non-canonical Wnt-signaling could have therapeutic applications, either alone or in combination with other newly developed targeted therapies that inhibit B-cell-receptor-signaling or BCL2. For this, we have the following specific aims: (AIM 1) Interrogate the signaling-pathways of non-canonical Wnt receptors in CLL - We will define the proteins recruited to ROR1/2 in response to Wnt5a and determine the structural domains required for signaling. We will examine the contribution of RYK to Wnt5a-signaling in CLL, determine the role of SH3-binding proteins, 14-3-3?, or Ca2+/calmodulin (CaM)-dependent protein kinase II (CaMKII) in ROR1-dependent signaling, and examine the contribution and function of ROR1 kinase to non- canonical Wnt-signaling. (AIM 2) Examine CLL cells for co-expression of non-canonical Wnt-receptors and determine the relative levels of Wnt-signaling - We will examine the blood samples of pts with CLL cells that have high, low, or negligible expression of ROR1 for plasma Wnt5a, leukemia-cell expression of ROR2 and RYK, and for leukemia-cell activation of canonical and non-canonical Wnt signaling. We also will examine the transcriptomes of selected CLL samples and cell lines for the newly described stemness index, which is dependent on ROR1-signaling. We also will examine for cross-talk between the canonical ?-catenin- dependent Wnt-signaling pathway and the non-canonical, ?-catenin-independent pathway, which may be influenced by the relative expression of ROR1, ROR2, or RYK, or by treatment with newly generated mAbs specific for ROR2 or RYK. (AIM 3) Examine the contribution of ROR1-signaling to the development of resistance to targeted therapies in CLL - We will examine expression-levels and function of ROR1, ROR2, and RYK in serial CLL samples collected from pts before, during, and after development of resistance to targeted therapies and evaluate the potential for synergy between cirmtuzumab and the BCL2 antagonist, venetoclax.